Naturally occurring human antibodies with specificity for light chains of immunoglobulins

Human sera of different categories were screened for antibodies against IgA. A surprisingly high incidence of antibodies was observed. All of these antibodies were of restricted specificity, i.e. able to react with one or a few individual IgAs from a panel of eight myeloma proteins used in the screening. In one serum of a patient with selective IgA deficiency an antibody against the allotype A2m(1) was found. Some of the antibodies were shown to belong to the IgG class. The IgA, IgG and IgM content of the antibody-containing sera was generally increased. Two different antibodies which both reacted with the same individual IgA were studied in detail. The antigen involved could not be detected in normal Caucasian sera but was detectable in some sera of patients with IgA, IgG, IgM or IgD paraproteinemia. The antigenic site was located on the light chain of the Ig molecule but no correlation with either the light chain type or the genetically determined Inv factor was evident.